Hello. I want to play around with the process of one photon splitting into more lower energy photons and vice versa. As I understand it one can quite easily make a Feynman diagram of a photon splitting into two lower energy photons by interacting with virtual electron/positrons. And also the reverse diagram is possible. Questions: - Once after getting the Feynman amplitudes for the splitting process, can one use the golden rule for Decays in a straight forward manner as one could for weak decays? - Which diagrams are more dominant? Is it sufficient to just use gamma -> gamma gamma, or is it necessary to for instance also include gamma -> gamma gamma gamma.